Magnetic material



June 1 1926.

,124 if 4f G. W. ELMEN MAGNETIC MATERIAL Filed May 5l 1921 2 Sheets-Sheet l 'Illia' Il Il lll June 1 1926. 1,5362@ G. w. ELMEN y MAGNETIC MATERIAL Filed May 51 1921 2 Sheets-Sheet 2 Patented .lurie .1, 3.926.

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' UNITED STTESPATENT GUSTAF W. ELMEN, OF LEONIA, NEW JERSEY, ,ASSGNOR TO WESTERN ELECTEEC PANY, INCORPORATED OF NEW YORK,

N. Y., A GOEPORATIQN OF NEW MAGNETC MATERL.

Application tiled may 31,

This invention relates to the production and use of a new material or 4substance having certain desirable magneticqualities, .among which are high magnetic perme- 5 ability, especially at low magnetizing forces, and low hysteresis loss. It is one object of this invention to provide a suitable loading material Jfor signaling conductors to increase their range and speed of operation. Another object relates to applying this loading material to 'a conductive core in amanner to produce a highly efficient transmission line for long range, high speed signaling. These objects and other objects will become apparent on consideration of examples of practice thereunder which will he disclosed specifically in this specicat-ion, with the understanding that the definition of the invention Will be given in the appended claims. This application is in part a continuation of application, Serial No. 111,080, filed July 24, 1916.

The importance of iron inthe practical application of electricity is Well known and has often been remarked upon. Its unique quality of high magnetic permeability has made it indispensable for the cores of tractive electro-magnets for dynamos, motors, VSCI telephone receivers, telegraph relays, etc. For this purpose it may, in certain cases, be advantageously united With a very small proportion of some other element, for ex ample. silicon. lNith this qualification it 85 may truly be said that the high permeability of iron makes it practically the only medium to be considered for the translation of energy of the electric current into useful mechanical effect, and for the reciprocal translation of mechanical energy into elec-- tric current. In dynainoelectric machines it is common to have laminated -iron cores subject to resultant magnetizing forces of the order of 2 to 5 or more c. g. s. units and to develop magnetic fluxes in these iron cores of the order of 10,000 to 20,000 lines per `square centimeter of cross-section. Much attention has been given to obtaining a quality of iron of' high permeability for iiiagnetiziiig forces and flux densities of the,

orders here mentioned. On this quality of ironl depends its effectiveness in most electroma giiets,

land copper.

v192i. 'serial No. 473,87?.

position of about 2A; nickel and /g copper, when tested at low magnetizing forces. gives a permeability higher than that of iron alone. It will be seen that with the exception ot aluminum, all these metals stand close together in their atomic weights and lt has been ifound that comsiderable extent by lamination, but the resistivity of the material is a factor that may be of importance in this connection; the higher the resistivity, the more the eddy current loss will be ke t down.

Magnetic material as important uses to advantage.

saine; Fig.

.an ideal way to improve signaling conductors would be by continuous loading, that is, by enveloping the conductor with a layer of magnetic material throughout its length. One trouble has been that with the lowmaguetizing forces found in signaling conductors, and the low permeability of known magnetic materials at these forces, the induction in the loading layer was too slight to be useful for long telegraph cables. Gen-v erally speaking, it was found that better resuits in transmission would be secured by devotingr the available cross-Section entirely to coppe-r instead of part to copper With the remainder an iron layer. Accordingly, to

y the present time, although there have been many suggestions for continuous loading, it has been found of no advantage for any purpose except for a' few comparatively short, submarine telephone transmission lines. In a few instances of this class, vcontinuous loading with iron has been employed advantageously. lt has not been made useful hitherto in telegraphy.

vThis invention provides a new magnetic material comprising elements of the magnetic group combined in suitable proportions, which, when subjected to a proper heat treatment and iarded against undue stresses and other disturbing causes develops and retains an extremely high permeability at low magnetizing forces, and a low hysteresis loss. This material has furthermore been applied with advantage to 'the continuous loading of signaling conductors in such a manner as to obtain the full benelits of the'above noted desirable properties.

'lhe practice of this invention compre# hends considerable variety in the composil tion and preparation of the magnetic material, the manner of its application for load ing material and other purposes, the safeguards against impairment of its magnetic property, etc. fin example of procedure, according to the invention, will now be disclosed by -which its utility may be realized rllhis disclosure will be made specific to this example, with thennderstanding' that generic aspects of the inven tion may comprehended in the terms of the a'gjrnendcd claims.

Referring to the accompanying drawings, Figure l is an elevation of a conductor loaded with the improved magnetic material of this invention; Fig. 2 is a cross-section of 3 is a cross-section saine A described, has

l l 1,586,884 tu conductorembodied in a submarine cable; Fig. .4 is a section of a furnace for heating the loaded conductor; Fig. 5 is a curve showing the relation of resistivity to per centage composition for a certain loading: material of my invention; Fig. 6 is a curve for hysteresis loss; Fig. 7 is an elevation of a conductor Wrapped doubly `With the magnetic material; Fig. 8 is a curve showing the permeability-temperature characteristics for a variety of the magnetic material; and Fig. 0 shows a loading coil With its core of this material and its winding indicated diagrammatically.

Iron and nickel arefused together in an induction furnace in the proportion of about 211/2 per cent of iron and 781/2 per cent of nickel. Good commercial grades of these two kmetals are suitable for this purpose. The molten composition is cured in a mold andcooled to form a thick ar or rod. This is subjected to repeated swaging operations by which it is reduced in diameter and correspondingly elongated. The long rod thus formed is then drawn out by repeated Wire drawing operations to a size of about No. 20 ld. and S. gauge. This Wire is then passed between `flattening rolls, land by several such operations, it is flattened to a tape of the -thickness of about 0.006 inch and width a little more than l0.125 inch. This tape is passed through cuttin T rolls or discs which trim its edges squarely on both sides and give the tape an exact and uniform Width. This tape of nickel-iron composition is now ready for application upon a conductor.

The stranded copper conductor of Figs. 1 and 2 comprises the central cylindrical wire enveloped by six equal helical strands 2, which are shaped to fit together' closely to form a cylindrical annulus about the Wire. lt is desirable that the conductor assembled in this Way shall have a smooth cylindrical contour, and for this-purpose it may be drawn through a die or subjected to a swag ing operation. The stranded conductor as the advantages oli flexibility and preservation of conductive continuity in case of a breakage by any stress not severe enough to interrupt all the strands at the same place. This stranded conductor l-2 is of size No. 5 l. and S. gauge, and is to be loaded with the improved magnetic material in the 'form of the tape heretofore described.

The nickel-irontape 3 is Wrapped helically on the stranded copper core, care being taken to abut the edges closely without lapping.

The taped conductor is next to be heattreated. For this purpose it is drawn lengthwise straight through the furnace ot Fig. 4f, which is maintained at a temperature of about 875 degrees centigrade. This is ,a inue `urnace with the heating elements 20 :tot

llZl) the tube 23-24 it cools in the air, which the ,proper rate 'of cooling. After heating in the outside the tube 423)--24 is at about normal room temperature, that is, about 20 .degrees centi rade. Under the conditions and "for imensions as'described, this givesa furnace-the conductor should belled away straight from the furnace far enoughffor it to become well cooled; bending at this stage may impairits high permeability. Also, the

'necessary coiling thereafter should be on a large radius, not less than 2 feet; the stresses and strains involved in coiling and uncoiling on a smaller4 radius may spoil the permeability. f

To develop the utmost possible permeability according to this invention, the rate of cooling after the heating in the furnace is a .matterof considerable importance. Forl the signaling conductor above described, .the iitiiiost possible permeability is not particularly'desirable, and an effective permeability 'of 2400 which is sufficient for lthe purpose, will be developed vby cooling in air as the taped conductor emerges from the furnace. For soniecases, of. which an example will be described later, amore exact procedure with respect to the rate of cooling, is contemplated. Aft-er they heat treatment, the taped or loaded conductor is insulated,l armored,

and mechanically reinforced, accordin to the u'sual practice for submarine cables,

y surrounding it 'with a layer of gutta percha and the usualrwrapping of'jute and the sheath of adjacent'4 helical steel wires, 'ving the product shown in cross-sectionfin ig. 3.

While a certain speed and temperature with acertain typefof furnace have been described t'o produce'the desired results in the casey of a particular conductor, it is apparent fthat these vfactorsmay be varied or adjusted to meet different cases, -such for example, as a conductor of difieren-t diameter from ythat here discussed While 781/2 percent and-21.1/2fper cent have been mentioned as giving'the proportion of the ingredients,l nickel and iron, to be employed in making up'- the improved magnetic material,it Will be understood that the 'proportion may deviate considerably lfrom these iigures when nickel'and iron are the only' ingredients, and vthat when 'there are otlieringredients, this proportion may not apply. Up to the present tin-ie when the only ingredients are nickelv and iron, 'it has been found that a proportion about the same as that named, gives the highest meability for low magnetizingforces. @their ingredients than nickel and iron may he eniployed for various purposes,v not! en -ry' to confer high permeal'iility one the product but for other objects; for exam-ple, it may be desirable to add chromuiii for the reason that a. comparatively small quant-ity' et: thisv clement will cause a decided` increase in the. resistivity cf the composition, andthrs high, resistivity n-iay be a desirable factor- 'o. ont

. doivii the eddy current losses in the iced" o material. -A composition of niche-ll polii- -4 cent, iron 34 per cent, and chromium il per A cent has been carefully prepared, heat-4 -treated, land tested, and has been found to give a high value of permeability at low niagnetizing forces.

Then this material was tested inthe form of pancake coils hereinafter described, the

Ap'ermeability of the composition at very loef magnetizing forces Was.A 1000' or more, which is much higher than the figure foriron. A

superior silicon steel givesy a parmeabili-tyv at forces approaching zerd of on y about 400. Thus it will be seen that with. the addition of chromium in considerable quantity, the

composition still has'a decidedly higher perv meability than iron, though pei-l'iapi'rsomewhat less than might be attained if the chro'- :i

mium were not present. The. resistivity of u thel composition containingchromium, just referred` to, is 100im1erohms per cu.. ein., whereas, the resistivity of iron is only about l1' microhms per cubic centimeter, and thev resistivity of the composition of nickel TS1/l percent and iron 211/2 vper cent is'yabout' 17'- microhms per cubic centimeter (seeFig. 5).

f .Measurements of the permeability .of nickel-iron compositions of other propor'.

tions thanvthat here stated haveshown that the departure may be considerable without serious impairment of the permeability.

Thus, using pancake coils, for .per 'cent nickel instead of 7 81/2 per cent, after proper lheating and cooling, the permeability at forces approaching zero, is about 4100, and at a vn'iagnetizing force oli-0.2 c. the permeability is about 15,000 whereas for a' percentage of' 781/2 the respective values of permeability are 7000 and 38,500. It will be seen that these values are much higher` than for siliconv steel at the same magnetizing forces, which has respective permeabilities of only about 400 and 1500; Thusv a wide departure may be made from the prog. s. un itportionnamed, yet the eimeability at low u forthe'best materials of the prior art. v It has already been mentioned that after 'the proper heat treatment the composition should be guarded against undue stresses ,'magnetizing forces will o e far greater than and strains. lVhen the percentages are nickel TS1/ i and iron 211A), the material can he bent with less impairment of permeability' than when the percentages are respectively T0 and 30. vIn other words, the optimum percentage seems to be more rugged against impairment of permeability by stresses and strains than the other percentage. However, the difference is not marked and apparently, it the material can be guarded against stresses and strains, this ditl'erence is of no fgreat consequence.

'libe maximum attainable permeability for the .nickel-iron composition at percentages of TS1/ and 211/2 respectively for the nickel and iron has been between 0,000 and 0,000 for zero magnetizing forces. rlhis value, which is designated the initial permeability, is lobtained by determining a series of valuesv for exceedingly low forces, say of the order ot 0.0L to 0.05 c. g. s. units. rl"he results plot linearly, and ma;v be extrapolated back to the value for llzt), thus giving the value ,ot the permeability at zero magnetizing i'orce.' The maximum permeability so tar vattained is between -l,000 and 60,000. This oef-,urs with the 781/2 per cent nickel composition ata magnetizing force of about 0.1

-best magnetic material previously known,

here entersI into the composition only to the cx-tent of less than a fourth part.

Y lt is worthy ot note thatthe proportion ot fthe ingredients of the nickel-iron composi- Mii tion which gives maximum permeability at lon7 forces and minimum hysteresis loss is also the proportion that gives zero magneto-striction in Ystrong magnetic fields (Hzl) lo H2500). liVhile the heat treatment may not necessarilyv be the same for the manifestation ot' these phenomena. the coincidence ot the proportion is significant ot a tundamental unique character in the composition which attains its maximum expression at that proportion.

The resistivity ot' the nickel-iron composition ot this invention is considerably higher than that ot either ot its components. and corresponds approximately to the curve given in Fig.v 5. Thus at 781/2 per cent nickel it will be seen that the resistivity is tullg.Y per centvhigher than tor either nickel or iron alone,

Evidently a smaller proportion of nickel gives a decidedly higher resistivity and it may be desirable in certain cases to sacritice permeability for the sake 0f resistivity. Mention has already been made that or some purposes the utmost attainment of pern'ieability is not necessary, and in such cases it may be better to decrease the proportion of nickel so as to give a point higher up on the curve oi Fig. 5. The resistivity when the nickel content is 30 or 35% is seen to be about 75 and for 25% nickel, at about which point the permeability ot the alloy at low magnetizing forces begins to be greater than for iron, the resistivity is about 30, that for iron being about 10.

Fig. 6 shows the hysteresis loss for actual samples of the improved composition for percentages of nickel varying over a wide range. The ordinates in this curve give the work in ergs per cubic centimeter represented by the usual hysteresis loop for a maximum induction of 5,000 c. g. s. units per square centimeter of cross-section.

lt will be seen that at 781/2 per cent nickel, the value is as low as 100 ergs. It will be noted that this percentage for minimum hysteresis loss is the same as for maximum permeability. The low result for the nickeliron composition at this percentage will be seen to be much lower than the values for othermagnetic materials. Thus for a superior quality of iron, the value is as high as 025 and for nickel it is no less than 2,200

A description has been given of the dimensions of the conductive core and the width and cross-section of the loading tape specifically for a certa-in contemplated example of along ocean cable for high speed telegraph transmission. ltwill be readily understood that the thickness of the tape and other factors may be altered to suit various cases. In some cases Where a thicker sheath is desired, it may be best to apply it in the form ot two tapes wound in opposite directions, one outside the other as indicated in Fig. 7. Among the advantages of this construction .are that it applies the loading sheath in two laminae instead of one, thus reducing the eddy current losses. Also,the opposite winding gives a somewhat more rugged structure tor handling, the tape being less likely to slip or buckle.. When more than one lamina of loading material is used, the thin coating et oxide on each serves as insulation to reduce the eddy currents, but other insulating coatings may be applied to the loading material if desired.

An ocean cable, 2000 nautical miles long, and loaded as described, may be operated as a telegraph conductor at a one-Way speed, approximately ten times as great as tor the present one-Way operation of unloaded ocean cables of that length. No ocean telegraph cables have heretofore been loaded,

loo

either continuously or by loading coils. With the loading materials heretofore available, it was better to fill the available cable cross-section Within a given insulating envelope entirely with copper, rather than to devote part of that vspace to loading inaterial. By this invention thereis provided -a magnetic material of such high permeability that it is advantageousto cut away part of the copper within the available crosssection, that isto cut away a cylindrical shell only 0.006 inch thick,'and replace it by this material. By this means the speed of the long telegraphfconductor may be increased in the ratio just mentioned.

The copending application of Oliver E. Buckley, Serial No. 492,725 filed August 16,

1921, discloses and claims a long submarine telegraph cable loaded with the material of this inventioin The mere intimate union of the ingredients of the new magnetic material may not be sufficient to cause it to exhibit the useful property of high permeability at low magnetizing forces to the degree mentioned. Proper heat treatment may be Anecessary to attain that degree of permeability.

In general, so far as investigations have gone, it has been found preferable to heat the described nickel-iron composition at least as hot as 825o C. and then cool it down at the proper rate, not too fast but fast enough. This proper rate of cooling is attainedin the example described specifically, by a rather ordinary procedureof cooling in air. Y

The foregoingdiscussion of the matter of the heat treatment affords guidance by its detailed presentation of a specific example, but it may be helpful to go over the matter for a different example.

Assume that one has obtained a composition of the desired ingredients in the desired percentage relation, but that he. does not `know what its previous history has been with respect t'o heat treatment, and that he wishes to develop the utmost permeability for low forces. It has been foundv convenient for testing purposes to take lengths of something like 4() feet of tape of crosssection 0.125 inch by 0.006 inch and Wind these lengths into pancake coils about three*` inches in outside diameter with a layer of paper between the successive turns. The paper may then' be expelled with an air blast, thus assuring that the turns of the metal tape are sufiiciently loose to guard against undue stresses and strains therein. These pancake coils are evidently convenientlyavailable for testing for permeability by the well-known method involving the use of a ballistic galvanometer. The first step will beto heat a series of specimens of this composition to a temperature around 900 degrees centigrade and hold them there for a long enough time to be assured that they have attained this uniform temperature throughout. There will be no objection to heating the specimens somewhat hotter and it may be easier in this Way to become assured that the temperature is suficicntly high throughout.

The improved magnetic material here under discussion has a so-ca-lled critical temperature or magnetic transition temperature, like iron and other magnetic materials. If it is heated from ynormal temperature to higher and highertemperatures and subjected to low magnetizing forces its permeability increases to a peak and then falls ofi' and vanishes very abru tly and the temperature.` where this last c ange takes piace is the so-called critical temperature (page 116 of the 1900 edition of Ewings Magnetic Induction in Iron and Other Metals). This magnetic transition temper ture for the improved magnetic material, f this invention will be considerably below the temperature ol' 900 degrees that has just been mentioned in a preceding paragraph, and it will be different for different compositions, and when' the ingredients are nickel and iron it will be different for different proportions of the ingredients. Generally speaking. this magnetic transition temperature will lie around 500 degrees C. or 000 degrees C. and may be somewhat more or less than these figures. f

Having heated the specimens thoroughly to a temperature of at ieast 900 degrees C.. they are next cooled down to a temperature near this magnetic transition temperature. preferably a temperature a little higher than the magnetic transition temperature. For a composition of nickel and iron only, with from o5 per cent nickel to 80 per cent nickel. this critical temperature will lie between 550 degrees C.' and G25 degreesC. The rate for cooling from 900 degrees C. down tc this point should be conveniently gradual say twenty minutes may -be required foi this stage with a pancake coil of loose'y wound nickel iron tapey as heretofore de.- scribed. No harm can be done by cooling too slowly through this sta-ge from 900 de grees down.

Next the specimens are to be cooled dowr through a temperature zone that will carry them distinctly lower than the magneti( transition temperature ata rate which is def siredl to be fast enough and yet not too fast Assuming as heretofore suggested, that the test is being made with a whole series of like specimens treated alike to the pointhof cooling down to the magnetic transltlon temperature, these specimens may be cooled at different rates from that pointv down to sav about 300 degrees, then cooled at any composition of 70 per cent nickel. When subjected to a constant magnetizing force of.

1110.03 and hea-ted up according to the ten'iperatures represented as abscissae and with the corresponding values of permeability a plotted as ordinates, a curve like lt is obtained provided that the cooling from the critical temperature down was at the optimum rate. On the other hand, if the cooling wastoo fast or too slow, the curve may be like S.

This means that for a composition in which the high permeability has. been developed, the curve R Will exhibit a high value of induction for moderate temperatures but will drop to an intermediate minimum as at P before going to the Well known maximum Q that precedes the attainment of the critical temperature, which in this case is about 600 degrees. On the other hand, if the desired permeability has not been developed like S, showing no such intermediate minimum as at P.

To sum up briefly, the specimen should be cooled through the stage from the critical temperature down at a rate not too fast and yet fast enough to develop the highest permeability at normal temperatures with low magnetizing forces. This rate may be readily determined by testing aseries of specimens at different rates, and guidance may be afforded by noticing Whether a test according to Fig. 8 gives a curve similar to R, having an intermediate minimum as at P, instead of such a curve as S, having no such intermediate minimum.

In connection with the foregoing, it should v be remembered, (l) that for many purposes the, utmost permeability is not necessary nor desirable; (2) that the rate of cooling that gives the utmost ermeability is not exactly and narrowly etermined, but that other rates of cooling not Widely different will give almost or quite as great permeability, (3) that a little practice along the line of Fig. 8 will enable one very quickly to recogin this specimen the curve Will be niza the best procedure to obtain the utmost permeability, and (4) that if it is not convenientto carry a plurality of test samples through different rates of cooling, a single sample can be taken over the same temperature range in successive trials at the different rates; in this connection it will be noticed that when the optimum rate has been discovered, the reproducibility of the procedure enables the maximum permeability to be reestablished in the same sample or a like sample.

It may be important to protect the magnetic material from stresses after it has had its high permeabilityl developed by the proper procedure of heating and cooling. Thus, in the case of the loaded cable, it has been found that if an attempt is made to put the tape through a heating and cooling treatment and thereafter apply it to the conductive copper core, the permeability may be impaired. Apparently, the stresses involved in Winding the tape upon the conductive core have a tendency to destroy the permeability that has previously been conferred upon the material of the tape. Hence it has been found advisable to conduct the heat treatment after the magnetic material has been assembled in its operative relation to the electric conductor with which it is to be associated.

For the continuous loading of a signaling conductor it is important not only to secure high permeability of the loading material, but it is important that the permeability be uniform. It has required much investigation to determine the necessary conditions of treatment, and these conditions have been presented in this specification.

It has been stated above that it is desirable that the conductor within the loading envelope shall have a smooth cylindrical contour. One reason for this is that at ocean depths, When the cable is subjected to pressures of the order of 5,000 pounds per square inch, if the conductor surface were irregular, the magnetic material might be stressed and strained unequally by the great pressure. The effect on the material of the sheath might be to impair its permeability. Another advantage of the compact structure shown for the conductor, is that it has -less electrostatic capacity than if it consisted of loosely assembled strands.

The improved magnetic material of this invention is useful for other purposes than for the continuous loading of signaling conductors. It may be used advantageously for relay armatures and for frequency changers and modulators. It is also useful for lumped loading as well as for continuous loading. Choke coils of very high inductance and low resistance, may be made up in remarkably small volume, With consequent saving of material and labor in manufacture.

Coils with cores of this material have been found larticularly valuable tor use as magnetic shunts in sulnnarine cable telegraph i'eceiving apparatus. This material is also vgoed t'or transformer cores, especially those working at low magnetizing forces, such as input transformers for telephone repeaters.

For loading coils, small wire of the magnetic material is insulated and wound into a core in the manner heretofore known for making soft iron cores for loading coils. On this core the windings o the loading coil are mounted. Such a coil is shown in Fig. 9, with the c'ore 6, on whichthe coilV windings 7 and 8 are indicated diagrammatically. In order to give the core material stability or constancy in permeability, even though large currents are superposed on the loading coil circuit, the core may be provided with gaps tilled with non-magnetic material 9. The use of the improved magnetic material allows the necessary effective permeability to be secured even with theseA gaps present. The number and length ot 'these gaps may be regulated as desired. The windings of the Wire core 6 may be held together by wrapping the core with tape 10 of non-magnetic material, and the core sections on each side of the non-magnetic gaps, with the winding thereon, may be held together by clamps 11.

Ordinarily, the stresses or strains put upon the nickel-iron wire (assuming that this is the composition of the improved magnetic material employed for the core 6), will not seriously decrease its permeability, provided it has been properly heat-treated before winding, so as to develop its possible high permeability. But if it seems desirable, the formed core can be heated and cooled at the proper rate so as then to develop its permeability. A

What is claimed is:

1. A magnetic material characterized by a higher permeability than that ot' iron at magnetizing forces around gauss or less, comprising two elements of the magnetic group. v

2. A magnetic composition comprising at least two elements of the magnetic group and having maximum permeability at less than f gauss magnetizing force.

3. A magnetic material characterized by a higher permeability than that of iron at magnetizing forces ofy ,2D- gauss or less, comprising nickel and iron, and in which the nickel component is 25 per cent or more of the whole. i

4. A magnetic material characterized by a higher permeability than that of iron at magnetizing forces of {L of a gauss 'or less, comprising nickel and iron, and in which the nickel component predominates.

.5. A magnetic material characterized by a higher permeability than that of iron at nealing followed by cooling at a rapid rate from a temperature at or near the magnetic transition temperature.

7. A magnetic material having its hysteresis loss less thanQOO ergs per cubic centimeter for a loop for which the limiting value of the induction is 5,000 c. s. units.

8. A magnetic material characterized by a higher permeability than that of iron at magnetizing forces of $5 of a gauss yor less and lower hysteresis loss than iron, comprising at least nickel and iron ot' the magnetic group, the nickel being within a few percent of 781/2 percent of the nickel-iron content.

9. A magnetic material comprising two elements of the magnetic group, having a permeability higher than that ot iron at magnetizing forces of ,26 gauss or less, and in combination therewith an electric conductor in inductive relation to said material.

10. The method of developing high permeability at low magnetizing forces in a magnet-ic material which comprises annealing said material, bringing it to a temperature approximating its magnetic transition temperature, and then cooling at a rate intermediate an annealing rate and a rate at which undue stresses and strains would be set up therein.

1l. The method of developing high permeability at low magnetizing forces in a magnetic material which comprises the stepA of heating it above a certain temperature and then cooling it past that temperature at a rate intermediate an annealing rate and a rate at which undue stresses and strains would be set up therein. l

12. The method of developing high permeability at low magnetizing fortes in a magnetic material which comprises bringing said material to a temperature approximating its magnetic transition temperature, and then cooling at a rate intermediate that required for annealing and that at which undue stresses and strains would be 'aused therein. l

13. A transmission line loaded Jfor high speed signaling with a magnetic material comprising nickel and iron and having a higher permeability at magnetizing forces of a small traction of a gauss, than iron.

l-l. Magnetic composition consisting chietly of nickel and iron and having a higher initial permeability than iron, the nickel t the current therein are around 26 gauss or less.

16. A transmission line loaded with a magnetic material having a hysteresis loss less than 200 ergs per cubic centimeter for a loop 'for which the. limiting value of in f duction is 5.000 c. g. s. units. 15

17. A transmission line loaded with a magnetic material comprising nickel and iron havinga higher permeability at low magnetizing forces than iron and a lower hysteresis loss than iron.

i8. The method of loading signaling conductors which consists in surrounding a conductor Withmagnetic material, heating said conductor and said magnetic material to a predeterminedl temperature and then cooling, the loaded conductor being maintained in a substantially straight condition during said cooling.

19. A continuously loaded signaling conductor comprising a conductor surrounded by a plurality of layers of magnetic material, saidmagneticmaterial having a sur- Jface coating of oxide formed thereon to insulate the layers from each other and from the conductor.

20. A magnetic alloy comprising iron and nickel and in which the nickel component predominates, and having higher permeability than iron at low magnetizing forces developed therein'by heating followed by cooling from a temperature at or near the magnetic transition temperature at a rate more rapid than the ordinary annealing rate vbut not so great as' to set up undue stresses in the alloy.

21. The method of loading a signaling conductor which consists in surrounding a conductor with magnetic material, heating the conductor with magnetic material thereon above a certain temperature, and cooling said conductor and magnetic material past that temperature at a rate intermediate an annealingrate and a rate at which undue stresses and strains would be set up in said magnetic material.

22. The method of loading a signaling conductor With magnetic material which comprises forming a layer of the material about the conductor, subsequently heating the magnetic material above its magnetic transition temperature, and cooling it at a 'rate intermediate that required to anneal and that Which Would give reduced permeability by setting up internal strains.

23. The method of loading a signal conductor with an allov containing nickel and iron, the permeability of which alloy at ordinary temperatures is dependent upon preceding heat treatment, which comprises surrounding the 'conductor With a layer of the alloy, subsequently heating the conductor and surrounding layer of alloy above the magnetic transition temperature of the alloy, and cooling it past that temperature at a rate intermediate that necessary to anneal and that Which Would set up undue internal strains.

24. A magnetic material characterized by higher permeability than SOO in the entire range of magnetizing forces from zero to 126 gauss, and comprising two elements of the magnetic group.

25. A magnetic material possessing a permeability above 800 in the entire range of magnet-izing forces from zero to 126 gauss, and comprising nickel and iron, in which the nickel component is 25% or more of the Whole.

26. A magnetic material possessing a higher permeability thanl 800 in the entire range or' magnetizing forces from zero to ,f2-6 gauss, and comprising nickel and iron7 in which the nickel component predominates.

27. A magnetic material characterized by a permeability above 800 in the entire range of magnetizing 'forces from zero to 1%- gauss, and comprising at least two magnetic elements, one oit which is nickel, and in which the nickel component is Within a few per cent of 781f% of the magnetic element content.

28. A magnetic material comprising two elements of the magnetic group, characterized by a permeability higher than 800 in the entire range of magnetizing forces between zero and 125 gauss, and in combination therewith an electric conductor in inductive relation to said material.

29. A transmission line conductor continuously loaded with a magnetic material comprising an alloy including nickel and iron, more than 25% of the Whole material being nickel, said material having an initial permeability above 300 measured on the conductor.

30. A transmission line conductor continuously loaded with a magnetic material comprising an alloy including nickel and iron, more than 25% of the Whole material being nickel. y

3l. A magnetic material comprising a nickel-iron alloy having an initial permeability permanently higher than 800.

32. A method of loading a signaling conductor with magnetic material, which comprises iiorming a layer of the material about the conductor, subsequently heating the magnetic material above its magnetic transition temperature, and cooling it at a rate intermediate that required to anneal and that which Would give reduced permeability by memes@ setting up internal strains, such cooling mie ing ci' nickel and; iron, the nickel being that which gives the material e perstantieily 781/2% of the total maite-rial, ait-' marient initial permeability above 800. the iron being substantially 2li/2% 33. A magnetic material characterized by total materiel. 5 a higher permeability than that of iron at. In witnees whereof, l liereune subscribe magnetizing forces of .2 of a geuss or less, my name this 26th de of Mey A. D., 1921., and lower hysteresis loss than iron, consist- Gr STAB W ELMENL, 

